There are many serialization formats (e.g. Apache Thrift) with versionable schemas. You can do a poor man's Thrift with json, mongo, etc. It's a common thing

There are many serialization formats (e.g. Apache Thrift) with versionable schemas. You can do a poor man's Thrift with json, mongo, etc. It's a common thing to throw thrift or protobuf values in giant key-value stores (cassandra, replicated memcache, hbase). You don't need to migrate unless you change the key format. If you want do on the fly migrations (mostly to save space, and have the ability to delete ancient code paths), you can do them a row at a time. And yes, we do occasionally write a script to loop through the database and migrate all the documents.